1. Field of the Invention
The present invention generally relates to a method for reducing cobalt leaching from metal working tools comprising cobalt, such as metal working tools comprising tungsten carbide particles bonded by cobalt, by contacting the metal working tool comprising cobalt with one or more triazoles which comprise at least butyl-benzotriazole in an amount effective to reduce such cobalt leaching during a metal working process from the metal working tool. The present invention also generally relates to a composition comprising a metal working fluid and one or more triazoles which comprise at least butyl-benzotriazole in an amount effective to reduce cobalt leaching from a metal working tool comprising cobalt, such as tungsten carbide particles bonded by cobalt.
2. Related Art
A large percentage of industrial cutting tools used to drill, cut, grind, and mill metals are made of tungsten carbide particles held together by a cobalt bonding agent. The mechanical working of hard metals, such as cemented carbides containing cobalt, by, for example, grinding the cobalt-containing hard metals, is often carried out in the presence of a metal working fluid (sometimes referred to as a “cutting fluid”). Metal working fluids may fulfill one or more functions in various metal working applications. These functions may include removal of heat from the work piece and tool (cooling), reduction of friction among the metal chips, tool and work piece (lubrication), removal of metal debris produced during the metal working process, reduction or inhibition of corrosion, reduction or prevention of the build-up of material on edges between the workpiece and the tool, etc. For example, in drilling, cutting, milling, etc., this metal working fluid may act as a coolant and/or lubricant at the area of contact between the metal surface being machined (worked) and the drilling, cutting or milling tool.
Although water or mineral oil may be used alone as a coolant or lubricant, the practice has been to add compounds to the metal working fluid to increase the lubricity and cooling ability of the fluid and to delay its deterioration. For example, these metal working fluids may include an additional lubricant, such as a fatty acid salt, and may also contain iron corrosion inhibitors, such as salts of triethanol amine. Some amines including alkanolamines and arylalkylamines such as p-benzylaminophenol have also been found useful in metal working fluids as antibacterial agents. See EPO 90-400732 to Noda et al. which is referred to in the Background section of U.S. Pat. No. 6,706,670 (Kalota, et al.), issued Mar. 16, 2004. See also U.S. Pat. No. 4,144,188 to Sato, issued Mar. 13, 1979 (also referred to in the Background section of U.S. Pat. No. 6,706,670) which adds to metal working fluids dissolving tablets containing primary amides, ethylenediamine tetraacetic acid, fatty acid esters, and alkanolamine salts to replenish such compounds during the useful life of the fluid.
When cutting, drilling or milling tools which are made up of tungsten carbide particles bonded with cobalt metal are exposed to these metal working fluids, the cobalt may be leached away. Leaching of the cobalt matrix from the tool leaves a residue of carbide particles and may result in premature failure of the tool. This problem of cobalt leaching may be further exacerbated by the metal working process itself. During metal working, a large quantity of metal chips may be produced having a large surface area which, when exposed to the metal working fluid, participate in the corrosion and leaching processes, such that the content of ionic cobalt in solution in an aqueous metal working fluid may reach levels several hundreds of milligrams, per liter of metal working fluid. See Background section of U.S. Pat. No. 4,976,919 (Skold et al.), issued Dec. 11, 1990.